An inkjet printer is a printing machine using a system in which droplets of ink are directly sprayed onto a printing medium. In such an inkjet printer, there is a possibility that a gas dissolved in the ink is gasified due to a change in pressure inside an ink storage portion during printing so that a nozzle is blocked. As a result, there is a risk that printing quality is noticeably degraded. This risk becomes remarkable in a long-term use and a high-speed operation. In order to solve such a problem, it is effective to perform degassing to remove dissolved gas and bubbles from the ink. As a method of effectively degassing the ink, Patent Literature 1 discloses a method of continuously degassing the ink by attaching a hollow fiber degassing module using a hollow fiber membrane to an ink passage reaching an inkjet head from an ink storage portion.
The hollow fiber degassing module disclosed in Patent Literature 1 is an external perfusion type hollow fiber degassing module and a hollow fiber membrane bundle obtained by bundling a plurality of hollow fiber membranes is received in a cylindrical body. Then, the ink is supplied to the outside of the hollow fiber membrane and the inside of the hollow fiber membrane is depressurized to degas the ink, and the degassed ink is discharged from a discharge port formed in a side wall of the cylindrical body.